1. Field of the Invention
The present invention relates to a light receiving module for use in a light remote control system utilizing light as a signal transmitting medium.
2. Description of the Prior Art
In recent years, a light remote control system utilizing light such as infrared rays as a signal transmitting medium has been used for many indoor apparatuses such as audio apparatuses, air-conditioners and television receivers, since infrared rays are tolerable to noises and capable of transmitting a comparatively large amount of information for a short period of time. In the light remote control system, a light emitting diode is used on the light irradiating side, and a light receiving module is used on the light receiving side. In a light receiving module disclosed in Japanese laid-open Utility Model Application No. H1-102834, a light receiving device and a circuit device for amplifying an output signal of the light receiving device are provided on a printed circuit board and housed in a shielding case.
In the above-mentioned light receiving module, however, an electrical connection arrangement is complicated since the light receiving device and the circuit device are connected through the printed circuit board. Further, since the connection line is long, noises are apt to be picked up between the light receiving device and the circuit device. Moreover, since a printed circuit board is used, the space occupied by the light receiving module is large. To solve these problems, it has been tried to integrate a light receiving device and a circuit device on one semiconductor substrate. However, it has not yet been put into practical use. This is because with such an arrangement, an output and a response speed of the light receiving device are low and because the circuit device is apt to erroneously operate when light is irradiated thereto.
FIG. 1 shows a light receiving module disclosed in Japanese laid-open Patent Application No. H3-72730. In the figure, a light receiving device 91 and a circuit device 92 are provided on a printed circuit board 93, and are housed in a shielding case 94. A structure for removing noise signals is added to the light receiving module. That is, a mesh 95 is provided at a light input portion of the shielding case 94, and a light filter 96 is arranged inside the mesh 95. Thereby, a specific noise signal is attenuated. For example, when the light receiving module is used for a television receiver, the mesh 95 and the light filter 96 are designed so that a noise signal (the frequency thereof is in the vicinity of 16.6 KHz) from a flyback transformer is attenuated.
However, such a noise removing structure increases the number of required parts and complicates the arrangement of the light receiving device. Further, even a desired input light signal passing through the mesh 95 and the light filter 96 is attenuated by the noise removing structure. Furthermore, an overflowing current is apt to flow between a diffusion layer 97 and an insulating layer 98 in the light receiving device 91. Thereby, a predetermined output current cannot be obtained.
Moreover, an arrangement where a light signal is directed to a light receiving device through a transmission hole provided to the mesh 95 of a shielding case which covers the light receiving device has a predetermined directional characteristic with respect to an entering direction of the light signal.
That is, concerning a small-size television receiver, since a user is located in a direction toward which a display tube thereof faces, it is only necessary to receive a light signal coming from a range approximately 30 degrees on both sides of the direction toward which the center of the display tube faces. Since only light having passed through the transmission hole which is provided on a flat portion of the shielding case is received, it is sufficient to receive only light coming from the inside of a cone, which is a directivity range, formed by rotating a line which is at 40 degrees to the perpendicular with respect to the flat portion of the shielding case about the perpendicular.
Since apparatuses are becoming larger in size and there are more occasions where an apparatus is remote-controlled which is arranged in the vicinity of the ceiling such as a lighting apparatus, it is required to increase the angle of directivity. That is, concerning a 29- to 40-inch television receiver, it is required to enable the television receiver to be remote-controlled at any position in a wide range in a room so that a user can enjoy watching television anywhere in the room. Moreover, in a case where a lighting apparatus hung from the ceiling is controlled with a remote controller, it is required that a user having the remote controller can control the turning on and off of the lighting apparatus anywhere in a room. Therefore, for remote controllers for these apparatuses, a cone of approximately 90 degrees is required. In other words, it is necessary for the light receiving module to receive both a light signal coming from a direction perpendicular to the shielding surface and a light signal coming substantially from the side of the shielding surface and to detect them at a low S/N (signal to noise) ratio. However, the above-described prior art cannot satisfy such a demand.